The present invention relates to a thermal printer suitable for a word processor and a typewritter, etc.
In a conventional thermal printer as disclosed in Japanese Patent Laid-open No. 58-31787, for example, an ink ribbon is interposed between a recording paper and a thermal head, and ink on the ink ribbon is molten by a heat generating means of the thermal head to thereby record characters and symbols, etc. onto the recording paper. Further, in erasing the record printed on the recording paper, an erasure energy is applied again to the ink ribbon, and the record is bonded to the ink ribbon, thus effecting the erasure. In the prior art, as the printing and the erasing operation are carried out by using a single ink ribbon, a peeling temperature of the ink ribbon from the recording paper is noticed. That is, in the printing operation, the ink ribbon is peeled off from the recording paper at high temperatures of the ink ribbon, while in the erasing operation, the ink ribbon is peeled off from the recording paper at low temperatures of the ink ribbon. The prior art device includes a movable ink ribbon guide designed to cooperate with an arm to be driven by a solenoid on the downstream side of the thermal head in a scanning direction. In the printing operation, the movable ink ribbon guide is separated from the recording paper so that the ink ribbon may be peeled off from the recording paper just after passing through the thermal head. In the erasing operation, the movable ink ribbon is pressed on the recording paper on the downstream side of the thermal head in the scanning direction so that the ink ribbon is maintained in contact with the recording paper for a certain period of time until the ink ribbon is cooled, even after passing through the heat generating means of the thermal head.
However, as the movable ink ribbon guide is operated simutaneously with the arm to be driven by the solenoid in the above conventional thermal printer, a quantity of movement of the movable ink ribbon guide is defined by a stroke of the solenoid. Accordingly, upon pressing the movable ink ribbon guide against the recording paper in the erasing operation, a pressure contact force is greatly changed with a change in thickness of the recording paper and surface roughness, for example.
Furthermore, an operation speed of the movable ink ribbon guide is substantially the same as that of the solenoid, which is very high. Accordingly, upon pressing the ink ribbon guide against the recording paper, such a high-speed operation causes the ink ribbon to be drawn extra from a ribbon cassette, resulting in slack or cut of the ink ribbon.